Aircraft, both fixed and rotary wing, utilize numerous rotating components whose dynamic and static balance is paramount to safe and efficient operation. Component rotating speeds range from very slow, in the low hundreds of RPM for helicopter main rotor blades (.about.300 RPM for the UH-1 helicopter), to tens of thousands RPM for gas turbine engines (.about.21,000 RPM). Between these extremes are RPM speeds for propellers, drive shafts, tail rotors, gear boxes, transmissions, power take-offs, environmental control units, hydraulic pumps, generators, clutches, sprague clutches, drive belts, tachometer generators, etc.
The proper balance of these components during normal design speeds is a characteristic that is essential for aviation operations. Aircraft are traditionally lightweight and thus, undesirable out-of-balance vibrations, and their harmonics, can cause serious structural damage and degrade flight performance.
Serious out-of-balance conditions of rotating components can lead to significant vibration which can, under certain circumstances, lead to catastrophic component and/or aircraft destruction in a relatively short period of time.
The aviation industry spends considerable resources to ensure that rotating components are in-balance and optimally functioning. Vibration analysis is traditionally used to check engine and power train components. Strobe light analysis and manual flag tracking techniques are used to check rotor and propeller balance.
Many of the rotating components are connected to electric producing devices, e.g., generators. For example, on gas turbine and piston-driven engines, most are connected to two tachometer generators plus a systems power starter/generator. One tachometer generator is connected to the gas producing turbine and the other tachometer generator to the power producing turbine.
The aircraft system's power producing starter/generator is connected to the drive shaft, gear box or power-take-off. Both tachometer generators and the aircraft power systems starter/generator emit electric signals proportional to the RPM of the component being turned.
A helicopter's rotor system is connected to a transmission via a mast assembly where the output RPM is read by a tachometer run by a tachometer generator connected to the transmission. It, too, emits an electric signal proportional to the RPM of the main rotor and the drive shaft connecting it to the transmission. The helicopter transmission has a power systems generator connected to it on an accessory gear box.
A known vibration detecting apparatus for a helicopter is described in U.S. Pat. No. 4,181,024 to Leak et al. This apparatus uses an accelerometer to sense vibration, and preferably requires placing multiple accelerometers at suitable locations throughout the aircraft. Each accelerometer is read individually by switching from one to the other.
U.S. Pat. No. 4,524,620 to Wright et al. describes an in-flight monitoring system which uses transducers as vibration sensors to monitor vibrations at individual rotor blades.
U.S. Pat. No. 4,465,367 to Sabatier describes a strobe light apparatus for detecting out-of-track distances of helicopter rotor blades. The pilot is required to aim a strobe light at the rotating blade tips from within the cockpit. This device is apparently not capable of measuring subtle degradations of machine components.
Because of the myriad moving components associated with the aircraft's various mechanical systems, both for fixed wing (airplane) or rotary wing (helicopter), and mutually interfering vibrational signals, traditional vibration analysis techniques may not be capable of detecting subtle, individual component conditions. Also, strobe systems are inherently limited in the type of conditions they measure. Thus, a continuing need exists for improved monitoring and diagnostic methods and devices.